It is quite obvious that magic can explain both (in the case of the cavalryman, also training, particularly good equipment, perhaps. I have already written about them; they can be considered commando units, a slightly weakened but somewhat more numerous version of heroes. If heroes can be as strong as dragons, then it is not shameful for a knight to be twice as weak as that dragon. Or, we need to drastically weaken the heroes...)
Gargoyles seem to have been deliberately created ignoring all these rules. At the same time, this is a cheap and numerous Tier 2 unit, so it is easy to create such non-optimal things for mages.
However, in WGE, I still replaced the visual of the gargoyles.
Added 1 minute ago
I will stand up for the "puzanov" - typical peasants who, after working the land, were recruited; the logic and atmosphere are quite consistent, although they would look even more atmospheric as neutrals.